1. Field of the Invention
The invention relates to an optical transmission device, and more particularly to an optical transmission device applied for universal serial buses (USBs).
2. Description of the Related Art
With development of optical transmission techniques, optical-fiber transmission has advantage of transmission speed, transmission distance, and capability of resisting interference. This, optical transmission devices are widely applied for various application. Since the advantage of the optical transmission technique, more and more applications tend to couple hosts and devices through optical transmission devices, such that the hosts and devices with the conventional interface specifications, such as interface specifications of peripheral component interconnect express (PCIE) or universal serial bus (USB) 3.0, are capable of performing optical fiber communication through the optical transmission devices. In an optical transmission device, active optical cables (AOCs) are disposed on two electrical-to-optical/optical-to-electronic (EO/OE) transformation processing chips at the host-end and the device-end. Through the AOC, the host and the device can performs optical fiber communication without changing of hardware. However, there are some problems in current AOCs. A host and a device supporting USB standard are given as an example. When the host is coupled to a current AOC and the device is not coupled to the current AOC, the host believes that there is a device is inserted and issues a link training sequence for building a link with the device since the AOC has been coupled to the host. At this time, since the device does not coupled to the AOC in practice, the device does not response to the link training sequence. Thus, the host does not receive any response, such that the host enters an invalid mode. In order to lift the invalid mode, the user usually has to perform complicated setting or make the host to re-perform the boot procedure, which causes the user inconvenient usage. Moreover, even if the link between the host and the device is built through the AOC successfully, when one of them is detached from the AOC, the other one cannot detect this detachment event, and the state machine of the other one may operate at an inappropriate state.